1. Field of the Invention
The present invention relates to a power unit equipped with a belt-driven continuously variable transmission together with an internal combustion engine. More particularly, to a power unit for continuously varying the speed of a belt-driven continuously variable transmission with an electric motor.
2. Description of Background Art
A power unit equipped with a starter motor for starting the internal combustion engine separately from the electric motor for the transmission is disclosed in JP-A No. 2006-46324.
In the power unit disclosed as a mode for implementation in JP-A No. 2006-46324, the left side of a unit case constituting the crankcase of the internal combustion engine extends rearwardly to constitute a transmission case. A shift chamber accommodating a belt-driven continuously variable transmission is formed on the other side, in the right-and-left direction, of the transmission case from the crankcase, shielded by a transmission case cover.
The belt-driven continuously variable transmission achieves a continuous speed variation by moving a movable half pulley of a drive pulley around which a transmission belt that is wound thereby in an axial direction to vary the winding diameter of the transmission belt. An electric motor for speed change use is used for moving this movable half pulley.
Thus, the rotational driving of the electric motor for speed change use is transmitted to the movement of the movable half pulley in the axial direction via a reduction gear mechanism and a screw mechanism.
On the other hand, the starter motor is intended for rotationally driving the crankshaft via the reduction gear mechanism.
Both the starter motor and electric motor for speed change use direct the drive shaft in the widthwise direction of the body, and are arranged substantially horizontally in tandem with a rotational supporting part journaling the power unit on the body in-between in a side view.
With this construction, the starter motor and the electric motor for speed change use cannot be arranged close to each other, necessitating long wiring for either or both with a corresponding increase in cost, reducing the length in which bundled wiring is possible and accordingly resulting in more complex wiring. Further, this construction makes it impossible to integrate the fitting work of the two motors.
Moreover, the separate arrangement of the relatively heavy motors invites dispersion of the mass.
On the other hand, if a small and light-weight electric motor for speed change use is used, the reduction gear mechanism having a plurality of gears will be arranged intervening between the electric motor for speed change use and the drive pulley of the crankshaft with a view to enhance the torque transmitted by the electric motor for speed change use. Thus resulting in an increased distance between the crankshaft and the electric motor.
This means a problem that, if the electric motor for speed change use is arranged behind the starter motor, an interference with the constituent parts of the body (especially the rear wheel) will readily occur. Therefore designing a layout to avoid such interference with constituent parts is made troublesome.